The primary objectives of the Pittsburgh Center for HIV Protein Interactions (PCHPI), is to elucidate structural and functional interactions that occur during the process of HIV infection, in particular during the immediate post entry phase, in cells using structural biological approaches. Cutting edge light optical imaging approaches will play an important role in these investigations. Therefore, a central biological imaging core is an integral component of this proposal. The Core will be housed in the Center for Biologic Imaging (CBI), which is equipped to perform a continuum of optical methods including all types of microscopy essential to the PCHPI. Within the scope of PCHPI, the focus will be on highly sophisticated live cell imaging for tracking single particles. Our expertise in computerized image processing and morphometry will allow quantitative analysis of observed phenomena to corroborate subtle qualitative changes. Importantly, the CBI has several ongoing and intense interactions with PCHPI members as is reflected in the preliminary data section. Given the success of these interactions, we expect a continued expansion in the use of optical techniques through the PCHPI.